The overall objective of this work is to develop procedures for the synthesis of some sesquiterpene lactones which have been isolated from plant sources in recent years and which have been shown to exhibit significant antitumor activity. At present our work is focussed on synthetic approaches to two germacranolides, elephantin and eupacunin and to analogues which may be accessible via the synthetic routes developed. Approach to elephantin is based on ring cleavage of a (4.4.6) tricyclodecane substrate to a 1,5-cyclodecadiene. Approach to eupacunin is based on ring closure of a cis,cis-1,6-cyclodecadiene substrate, elaboration of functionality, and finally regeneration of the cyclodecadiene by 1,4-elimination.